It's not a cat problem or you'd have misfires on all cylinders. P0300 is random misfires, and the codes increment to show what cylinder is misfiring. P0301 is a misfire on cylinder 1, P0302 is cylinder 2, etc. You likely have a bad coilpack. Whichever cylinder is indicated, replace that coilpack.

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IT IS MISS FIRING YOU ARE CORRECT AND IF YOU GO TO ADVANCE, PEPBOYS. THEY WILL FIND A CODE FOR A MISSFIRE .THEN YOU START TO HUNT IT DOWN AND THINK, WHEN WAS THE LAST TUNE UP LOW FUEL PRESSURE OR BURNED VALVE . MAKE A LIST AND START THE HUNT

Sounds normal when you have a cylinder miss.The flashing light means the problem is serious.You would have the computer scanned for trouble codes then research the codes. You should get a code telling you which cylinder is not providing power and you check the ignition and fuel injector for that cylinder or cylinders.

you have a bad engine missfire. a flashing check engine light means you are in danger of damaging your catylitic converter and you should scan the car. most causes of missfires are plug wires and or coil pack.

If the check engine light goes on for any length of time, there probably are codes stored in the computer that can give you clues as to what is wrong with the electronic engine controls, or mechanical parts on the engine.Reading Codes 1985–94 vehicles
Codes are displayed by the MIL flashing ON and OFF. The time duration of the flash identifies the significance of the digit. Three flash durations are used:

A flash duration of 0.5 seconds indicates no malfunction (OK).

A flash duration of 1.3 seconds indicates that it is a 10's digit.

A flash duration of 0.2 seconds indicates that it is a 1's digit.

For example, if 3 flashes — 1.3 seconds long — are followed by 4 flashes — 0.2 seconds long — a Code 34 is indicated. These code sequences are separated by 1.8 seconds to avoid confusing tens and ones digits.

Read Memory Mode: used to pull codes which have been stored in memory. It is most effective in detecting poor contact of wiring harness connectors. To enter this mode, connect the read memory connector with the ignition ON.

D Mode: used to diagnose and test the entire injection system. To enter this mode connect the test mode connector with the ignition ON. On the Legacy and SVX, the ignition must be ON with the engine running.

F-Check Mode: used to measure the performance characteristics of the injection system components. When working in this mode, a Select Monitor or equivalent scan tool is required.

U Check Mode: operates during normal engine operation. It signals the driver using the MIL only when components necessary for start-up and drive are faulty. The read memory and test connectors must be disconnected with the ignition ON for this mode to be operational.

An EVAP code is emissions and should not harm the engine. A flashing check engine light is a bad thing. When it is flashing it is telling you it has a missfire bad enough to damage the catylist, converter or engine. I would worry about that more than any EVAP code. Good Luck